The present invention relates generally to semiconductor fabrication and more specifically to polishing semiconductor metal layers.
During metal/copper chemical mechanical polishing processes, three films/materials are encountered. 1) A patterned dielectric layer, usually silicon oxide (oxide), within which an opening is formed; 2) a barrier layer which lines the oxide layer opening and covers the top of the patterned oxide layer; and 3) a metal layer, usually copper, formed over the patterned dielectric layer, filling the barrier lined opening. In order to planarize, or polish, the metal layer to form a planarized metal structure within the barrier lined opening in the dielectric layer, a variety of polishing steps with various slurries are employed.
U.S. Pat. No. 6,217,416 B1 to Kaufman describes a first and second CMP slurry wherein the second slurry includes an abrasive, an oxidizing agent and acetic acid wherein the weight ratio of oxidizing agent/acetic agent is at least 10 and wherein the two slurries are sequentially used in a method to polish a substrate containing copper and containing tantalum or tantalum oxide or both tantalum and tantalum oxide.
U.S. Pat. No. 6,338,744 B1 to Tateyama et al. describe a high purity polishing slurry comprising water and dispersed silica particles.
U.S. Pat. No. 6,261,158 B1 to Holland et al. describes a multi-step CMP system used to polish a wafer to form metal interconnects in a dielectric layer upon which barrier and metal layers have been formed.
U.S. Pat. No. 6,447,371 B2 to Brusic Kaufman et al. describes a chemical mechanical polishing slurry useful for copper/tantalum substrates.
U.S. Pat. No. 6,313,039 B1 to Small et al. describes a chemical mechanical polishing composition and process.
U.S. Pat. No. 6,530,968 B2 to Tsuchiya et al. describes a chemical mechanical polishing slurry.
Accordingly, it is an object of one or more embodiments of the present invention to provide an improved method of polishing metal layers.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a structure having an upper patterned dielectric layer with an opening therein is provided. A barrier layer is formed over the patterned upper dielectric layer and lining the opening. A metal layer is formed over the barrier layer, filling the opening. A first polish step employing a first slurry composition is conducted to remove a portion of the overlying metal layer. A second polish step employing the first slurry composition is conducted to: polish the partially removed overlying metal layer; and to expose portions of the barrier layer overlying the patterned upper dielectric layer. A third polish step employing a second slurry composition is conducted to remove the exposed barrier layer portions and exposing underlying portions of the patterned upper dielectric layer. A fourth polish step employing the second slurry composition and BTA is conducted to buff the exposed upper dielectric layer portions.